A key prosecution witness at the Lockerbie bombing trial has been accused of changing his opinion of the facts to suit his theory of how Pan Am flight 103 was destroyed, reported BBC.online Thursday.

It said Professor Christopher Peel had earlier told the Scottish court in the Netherlands he calculated the bomb was 60cm (24 inches) inside the fuselage in a baggage container and weighed about 500 grams (one pound).

However, defense advocate Richard Keen referred to an earlier report by Professor Peel which used a different model to establish the location and size of the device.

Keen put it to him that he had changed his opinion of the facts to fit his new theory.

Professor Peel replied he had not done so consciously, as quoted by BBC.

Professor Peel, a chief scientist with the Defense Research and Evaluation Agency (Dera), explained that a reconstruction of the part of the plane where the bomb exploded was used to try to locate the source of the blast, the report added.

He said he applied a series of algebraic calculations to data describing the damage to the skin of the aircraft to work out the location and weight of the bomb.

He said only a unique combination of charge size and distance from the fuselage could have caused the damage he observed.

He added his conclusions were confirmed by a computer simulation.

On Wednesday, the court heard evidence relating to the cargo container believed to have held the suitcase containing the bomb.

They face alternative charges of conspiracy to murder and a breach of the 1982 Aviation Security Act.

They have lodged special defenses of incrimination blaming, among others, members of the Popular Front for the Liberation of Palestine - General Command

About 1,000 witnesses are expected to give evidence.

The trial could last for a year

Dera official Ian Cullis told the court the bomb could not have been in a case on the floor of a cargo container.

Cullis gave evidence on experiments into the effects of explosives on baggage and baggage containers within aircraft.

He said that pitting, which could look like a roughening of the surface, was caused by small particles from the explosion traveling at speeds of up to 2,500 meters a second (about 1.5 miles a second) – Albawaba.com